This invention relates in general to hybrid drive systems for vehicles and other mechanisms. In particular, this invention relates to an electro-hydraulic machine for use with such a hybrid drive system.
Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source of rotational power to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine generates rotational power, and such rotational power is transferred from an output shaft of the engine through a driveshaft to an input shaft of an axle so as to rotatably drive the wheels of the vehicle.
In some vehicles and other mechanisms, a hybrid drive system is provided in conjunction with the drive train system for accumulating energy during braking of the rotatably driven mechanism and for using such accumulated energy to assist in subsequently rotatably driving the rotatably driven mechanism. To accomplish this, a typical hybrid drive system includes an energy storage device and a reversible energy transfer machine. The reversible energy transfer machine communicates with the energy storage device and is mechanically coupled to a portion of the drive train system. Typically, the hybrid drive system can be operated in either a retarding mode, a neutral mode, or a driving mode. In the retarding mode, the reversible energy transfer machine of the hybrid drive system accumulates energy by braking or otherwise retarding the rotatably driven mechanism of the drive train system and stores such energy in the energy storage device. In the neutral mode, the hydraulic drive system is disconnected from the drive train system and, therefore, is substantially inoperative to exert any significant driving or retarding influence on the rotatably driven mechanism. In the driving mode, the reversible energy transfer machine of the hybrid drive system supplies the accumulated energy previously stored in the energy storage device to assist in subsequently rotatably driving the rotatably driven mechanism.
One commonly known hybrid drive system uses pressurized fluid as the actuating mechanism. In such a hydraulic hybrid drive system, a fluid energy storage device (such as an accumulator) and a reversible hydraulic machine are provided. Another commonly known hybrid drive system uses electricity as the actuating mechanism. In such an electric hybrid drive system, an electrical energy storage device (such as a battery) and a reversible electric machine are provided. Other hybrid drive systems are known in the art that use other actuating mechanisms.
Regardless of the specific actuating mechanism that is used, the hybrid drive system can improve the performance of the drive train system (such as fuel economy, for example) by recovering and storing energy during deceleration and by retrieving and supplying the stored energy for use during a subsequent acceleration. However, the hybrid drive system does not improve the performance of the drive train system during idle situations, such as when a vehicle in which the drive train system is provided is not moving. During such idle situations, the performance of the drive train system can be improved by turning off the engine. However, the drive train system may include one or more accessories that may be necessary or desirable to be operated while the engine is not operated. Such accessories can be electrically operated (such as lighting systems, navigation systems, audio systems, and the like), hydraulically operated (such as steering systems, braking systems, air conditioning systems, and the like), or a combination thereof. Thus, it would be desirable to provide an improved structure for a hybrid drive system that is capable of operating such accessories while the engine is not operated.